Abstract
The aim of this study was to perform a detailed analysis of the air kerma values around a Liac mobile linear accelerator working in a conventional operating room (OR) for IORT.The Liac delivers electron beams at 4, 6, 8 and 10 MeV. A radiation survey to determine photon leakage and scatter consisted of air kerma measurements on a spherical surface of 1.5 m radius, centered on the titanium exit window of the accelerating structure. Measurements were taken using a 30 cm3 calibrated cylindrical ion chamber in three orthogonal planes, at the maximum electron energy. For each point, 10 Gy was delivered. At selected points, the quality of x‐ray radiation was determined by using lead sheets, and measurements were performed for all energies to investigate the energy dependence of stray radiation. The photon scatter contribution from the metallic internal patient‐shielding in IORT, used to protect normal tissues underlying the target, was also evaluated. At seven locations outside the OR, the air kerma values derived from in‐room measurements were compared to measurements directly performed using a survey meter. The results, for a delivered dose of 10 Gy, showed that the air kerma values ranged from approximately 6 μGy (upper and rear sides of the Liac) to 320 μGy (lateral to beam stopper) in the two orthogonal vertical planes, while values lower than 18 μGy were found in the horizontal plane. At 10 MeV, transmission behind 1 cm lead shield was found to be 42%. The use of internal shielding appeared to increase the photon scatter only slightly. Air kerma values outside the OR were generally lower than 1 mGy for an annual workload of 200 patients. Thus, the Liac can safely work in a conventional OR, while the need for additional shielding mainly depends on patient workload. Our data can be useful for centers planning to implement an IORT program using a mobile linear accelerator, permitting radiation safety personnel to estimate in advance the shielding required for a particular workload.PACS number: 87.55.ne, 87.56.bd
Highlights
132 Ciocca et al.: Radiation survey around a Liac growth of dedicated treatment units, namely mobile linear accelerators, have changed the practice of intraoperative radiation therapy (IORT) in a significant way, by allowing a larger number of patients to undergo a normal surgical procedure and immediate irradiation without the need for transportation outside the operating theatre.Mobile linear accelerators are quite compact and designed to operate only in the electron mode up to 10-12 MeV, offering the great advantage that they can work in almost any conventional operating room (OR), with little or no added shielding, depending on patient workload.[2]Concerning radiation protection, the AAPM recently published recommendations for the implementation of an IORT program using mobile linear accelerators in a non-dedicated environment.[2]
At our Institute, the Liac is mainly used for IORT to the breast at doses ranging from 12-16 Gy up to 21 Gy, in all cases prescribed at 90% isodose.[9,10,11,12,13]
The dependence of stray radiation on beam energy was investigated at a point outside the primary beam path and air kerma values at 8, 6 and 4 MeV were found equal to 90%, 73% and 69%, respectively, of that measured at 10 MeV
Summary
132 Ciocca et al.: Radiation survey around a Liac growth of dedicated treatment units, namely mobile linear accelerators, have changed the practice of IORT in a significant way, by allowing a larger number of patients to undergo a normal surgical procedure and immediate irradiation without the need for transportation outside the operating theatre.Mobile linear accelerators are quite compact and designed to operate only in the electron mode up to 10-12 MeV, offering the great advantage that they can work in almost any conventional OR, with little or no added shielding, depending on patient workload.[2]Concerning radiation protection, the AAPM recently published recommendations for the implementation of an IORT program using mobile linear accelerators in a non-dedicated environment.[2]. 132 Ciocca et al.: Radiation survey around a Liac growth of dedicated treatment units, namely mobile linear accelerators, have changed the practice of IORT in a significant way, by allowing a larger number of patients to undergo a normal surgical procedure and immediate irradiation without the need for transportation outside the operating theatre. Mobile linear accelerators are quite compact and designed to operate only in the electron mode up to 10-12 MeV, offering the great advantage that they can work in almost any conventional OR, with little or no added shielding, depending on patient workload.[2]. The aim of this study was to perform a detailed analysis of the x-ray air kerma rates and the shielding assessment of a Liac (Info&Tech, Roma, Italy, http://www.sordina.com) mobile electron linear accelerator installed in a conventional OR. At our Institute, the Liac is mainly used for IORT to the breast at doses ranging from 12-16 Gy (in case of anticipated boost to the tumour bed and nipple-sparing mastectomy) up to 21 Gy (exclusive irradiation modality in partial breast irradiation), in all cases prescribed at 90% isodose.[9,10,11,12,13]
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